1. Field of the Invention
The present invention relates to a communication system and a method for performing short message services in the communication system, and more particularly, to a communication system suitable for third generation partnership project (3GPP) and a method for performing short message services (SMS) in the communication system.
2. Discussion of the Related Art
The technology for short message services provided under CDMA environment is based on short message standard IS-637. The short message services in a radio section are based on IS-95 and J-STD-008. For such short message services under the CDMA environment, a service center provides short messages, and a base station receives the short messages from a core network and transmits them to a mobile station through a control channel, i.e., a paging channel. The service center can transmit the short messages together with destination addresses and other service information, and the mobile station (i.e., user equipment) can receive the short messages in an idle state.
Furthermore, a global system for mobile communications (GSM) for multimedia services such as voice and audio data supports cell broadcasting of the short message services under radio environment. To this end, the European telecommunication standard institute (ETSI) suggests technical specification to realize cell broadcasting of the short message services.
The cell broadcasting of the short message services in the GSM broadcasts short messages from a public land mobile network (PLMN) to a user equipment (UE).
A 3GPP system will be described with reference to FIG. 1. The 3GPP system consists of a user equipment (UE) system, a network (or UTRAN) system, and a core system, and as shown in FIG. 1, each systems have bidirectional channels. (particularly, between the UE and the UTRAN.) In other words, the 3GPP system has an up link and a down link. Each system includes a higher layer, a radio resource control (RRC) layer corresponding to the lowest layer (layer 3), a radio link control (RLC) layer and a media access control (MAC) layer corresponding to layer 2, and a physical layer corresponding to layer 1. The physical layer provides different transmission channels to the MAC layer. The MAC layer provides different logical channels to the RLC layer. The transmission channels provided to the MAC by the physical layer are classified into common channels and dedicated channels according to information transmission mode on a radio line. The transmission channels have different characteristics depending on how information is transmitted on a radio line.
The logical channels provided to the RLC layer by the MAC layer have different characteristics according to transmitted information types. The MAC layer provides data transmission services (control data transmission or user data transmission) through the respective logical channels having different characteristics. Accordingly, the respective logical channels are divided into control channels and traffic channels depending on which information (for example, control data or general data) is transmitted.
The higher layer transmits a corresponding message to the RLC layer corresponding to a lower layer depending on service type selected by a user. The RRC layer controls logical connection of the lower layers (RLC layer, MAC layer and PHY layer) which provide services selected at the higher layer. To this end, the RRC layer is connected with the respective lower layers by a service access point (SAP) for control. The RRC layer is controlled by receiving and transmitting primitives through the SAP. Also, the RRC layer serves to confirm, maintain and release the connection, and serves to assign, reconstruct and release radio resources for the connection.
The RLC layer which received service messages from the higher layer controls radio link connection with a corresponding system. The RLC layer also serves to divide and reconstruct the received messages and compress header (RLC header), and serves to perform concatenation, padding, error correction, flow control and transmission of capsulated data units.
The MAC layer receives the capsulated data units from the RLC layer and analyzes their header to make MAC data units. The MAC data has radio characteristics suitable for radio interface and uses corresponding transmission channels depending on how data is transmitted.
The physical layer provides functions such as encoding and decoding of the transmission channels, multiplexing and demultiplexing of the transmission channels, modulation and spread of physical channels, demodulation and despread of physical channels, synchronization of chip, bit, slot and frame, power control, frequency processing, error detection, and transmission speed control.
Particularly, two messages for cell broadcasting of the short message services (SMS) are defined in the GSM. The two messages are SMS cell broadcasting (SMSCB) message and a schedule message.
FIG. 2 is a diagram showing a scheme of SMSCB message defined in the GSM. FIG. 3 is a diagram showing a scheme of a schedule message defined in the GSM.
In FIG. 2, the SMSCB message is of 88 octet unit, and each field is of octet unit.
There are provided a serial number field, a message identifier field, a data coding scheme field, and a page parameter field in the SMSCB message.
Also, the schedule message is of octet unit, and includes four successive blocks, as shown in FIG. 3.
The cell broadcasting of the SMS in the GSM includes a discontinuous reception (DRX) mode and a non-discontinuous reception (Non-DRX) mode.
In the DRX mode, the user equipment reads the SMSCB message using the schedule message only when a desired SMSCB message is newly renewed, and does not receive any message data for the other time.
On the other hand, in the Non-DRX mode, the user equipment can read messages of all frames. At this time, all the SMSCB messages can be read in even case that there is no separate information by the schedule message. The user equipment analyzes header of the SMSCB message and reads a corresponding available SMSCB message.
The aforementioned SMSCB message and the schedule message are adapted to radio environment in the GSM but are not adapted to next generation mobile communication. In other words, macro message transmission is expected in the next generation but each message in the GSM does not exceed 88 octet. Also, the SMSCB message does not exceed 15 pages and header should be accompanied for each SMSCB message corresponding to each page.
In order to apply the short message service provided under the CDMA environment or the SMS cell broadcasting provided under the GSM environment to the next generation mobile communication system which seeks global roaming service, much correction is required.
Particularly, the technical specification for the SMS cell broadcasting is required to be suitable for the 3GPP system which is the next generation mobile communication system based on the core network of the GSM and the radio access technology.
Accordingly, the present invention is directed to a communication system and a method for performing short message services in the communication system, that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a communication system suitable for a third generation partnership project (3GPP) radio environment and a method for performing short message services in the communication system.
Another object of the present invention is to provide a communication system capable of making short message without any restriction and a method for performing short message services (SMS) in the communication system.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the scheme particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a communication system according to the present invention includes: a radio link control (RLC) layer for dividing a data unit having a first length corresponding to short messages transmitted from a higher layer on a down link into data units having second lengths, and for reconstructing data units having third lengths transmitted from a lower layer on an up link into data units having fourth lengths; and a media access control (MAC) layer for multiplexing logical channels assigned for the data units having the second lengths on the down link with different logical channels, performing scheduling for the data units having the second lengths to obtain schedule messages, and demultiplexing transmission channels multiplexed from the lower layer on the up link.
In another aspect, a method for performing short message services (SMS) between a first communication system and a second communication system includes the steps of: (a) dividing a short message having a first length from a higher layer of the first communication system into data units having second lengths on a radio link control (RLC) layer of the first communication system; (b) multiplexing transmission channels for the divided data units with different channels at a MAC layer of the first communication system corresponding to a lower layer than the RLC layer, and performing scheduling on the multiplexed channels to obtain schedule messages; (c) transmitting the schedule messages and the data units to a second communication system through transmission channels corresponding to a radio interface section; and (d) selectively receiving the transmitted short messages from the MAC layer of the second communication system using information included in the transmitted schedule messages.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.